The invention relates to glide heads for evaluating the glide quality of a surface of a rotating disc. More particularly, the invention relates to glide heads with improved air bearing surface properties and to efficient methods for making glide heads.
Disc drives are used for storing information, typically as magnetically encoded data, and more recently as optically encoded data, on a disc surface. Glide tests are used to check disc surfaces for defects. In particular, glide tests are used by computer disc manufacturers to control and assure the quality of the disc media. Generally, all hard drive discs are tested before shipment. During a glide test, the glide head or slider flies over a disc surface generally at a predetermined clearance from the disc surface, known as the glide height or fly height.
If contact occurs between the glide head and a disc defect or asperity, the glide head vibrates and deforms. The vibrations can be measured with a piezoelectric transducer (PZT), which generates a varying potential difference between the electrodes of the PZT due to forces on the transducer. Specifically, when the glide head interacts with a defect on the spinning disc, simultaneously excited vibrational modes of the PZT and the head result in voltage fluctuations at corresponding frequencies. If the magnitude of measured voltages exceed predetermined threshold values, the disc may be rejected. Other types of transducers can be used such as thermal asperity detectors or capacitance detectors.
As storage densities on disc recording media become higher, fly heights of read/write heads generally become smaller. Lower fly heights impose narrower restrictions on acceptable heights of asperities/defects on a disc surface since larger defects would result in contact between the read/write head and the disc. Contact between a read/write head and a disc generally results in damage to the head and/or to the disc. The glide quality of a disc directly relates to the ability of a head to fly adjacent the disc at a fixed distance from the disc without colliding with a defect on the disc that results in a deformation of the head producing vibrations with a magnitude above a threshold value, as measured with the transducer. The glide quality of a disc is related to the disc smoothness, although other defects also may alter glide quality.
Glide heads generally are designed to have a fly height that is sensitive to the linear velocity of the disc surface relative to the glide head. To achieve measurements of smaller asperities on the disc surface, the disc velocity can be decreased to decrease the fly height of the glide head.
As the operating fly height or the glide height of the glide head decreases, it becomes necessary to tighten the tolerances on the parameters that induce variability in the glide head fly height. Parameters that add to the glide head fly height variability include the surface flatness and surface roughness of the air bearing surface of the head.